1. Field of the Invention
The invention relates to an image processing apparatus that performs image processing for image data, and an image processing method and an image processing program that can be used in the image processing apparatus.
2. Description of the Related Art
To record original image data made up of R (Red), G (Green), and B (Blue) components provided by reading an original image through a scanner in a printer in a scanner, etc., it is a common practice to convert the original image data into C (Cyan), M (Magenta), and Ye (Yellow) components in accordance with color components of ink used for recording and then generate a K (Black) component from the C, M, and Ye components and subtract the K component from the C, M, and Ye components to execute under color removal (UCR), thereby generating a record image made up of the C, M, Ye, and K components.
In the area represented in black in the original image, color spreading occurs in the edge portion (boundary between black and any other color than black) if the record positions of C, M, and Ye components shift slightly in the record image.
Thus, in recent years, the color component generation method using under color removal has been changed between the edge portion and any other portion so as to decrease the C, M, and Ye components in the edge portion more than those in any other portion. Accordingly, the percentage of the C, M, and Ye components in the edge portion becomes lower than that in any other portion, so that occurrence of color spreading caused as the record positions of the C, M, and Ye components shift can be suppressed.
To execute such under color removal, it is necessary to determine whether or not each of the pixels making up an image is a pixel forming a part of an edge portion in a black area. However, it is generally difficult to accurately determine whether or not the pixel is a pixel in the edge portion, and the pixel not to be determined a pixel in the edge portion may be erroneously determined a pixel in the black area.
For example, as for pixels making up a dot area, the pixel indicating each dot in the dot area is easily determined erroneously a pixel in an edge portion.
If the pixels making up a dot area are thus erroneously determined pixels in an edge portion, the percentage of the K component in the pixels increases and therefore the record image has the area corresponding to the dot area recorded in improper dark color, and the original image is not faithfully reproduced.
To prevent such an erroneous determination, for example, if no edge pixels exist in the pixel periphery determined an edge portion, it is possible to enhance the accuracy of the determination according to an art wherein the corresponding pixels are determined pixels making up an area represented in halftone rather than the edge portion (JP-A-H3-213057), an art wherein whether or not pixels detected to be pixels making up a character based on the edge density using continuity of a line forming a character are correct is determined from the peripheral pixels (surrounding pixel information) (JP-B-3100383), or the like.
JP-A-H3-213057 and JP-B-3100383 are referred to as related art.
The above-described arts can enhance the accuracy of the determination, but are not sufficient to prevent the original image from being unfaithfully reproduced because an erroneous determination can occur.